Craig - Sorry about the initially thought incorrect advice on the Jim Carter part. The correct one listed for Chevrolets from Jim Carter should be
ME727 and as you noted they are out of stock.
A peek in some Chevy Master Parts books shows the original part is listed as Parts Group 0.533, Bearing, camshaft thrust GM# 3702305 fitting ALL 1937-53 6 cylinders. That part number was later replaced by GM# 3707916 which began in 1954 and is further listed as fitting 1938-62 6 cylinders.
Interestingly enough, GM# 3707916 is also listed in a 1963 GMC Master Part Book as used for 248-270-302 6 cylinders from 1955-59. It sounds like perhaps the GMC listed part from Jim Carter might actually be one that would fit your application.
The spacer rings are listed for all applications.
